Dual cure polyurea coating composition

ABSTRACT

A two component polyurea coating composition that exhibits a dual cure phenomena. The coating composition comprises a polyaspartic ester that is combined together with a polyisocyanate in such a manner that the polyisocyanate is present is an amount that is greater than a normal stoichiometric amount for the polyaspartic ester. By over indexing the polyaspartic ester with the polyisocyanate advantages of moisture curing and or “fast curing” can be combined together in the final finish.

BACKGROUND OF THE INVENTION

The present invention relates to a polyurea coating composition that canbe applied as a wet finish on any substrate. More particularly, thepresent invention relates to a two component polyurea coatingcomposition that exhibits a dual cure phenomena.

Two component coating compositions containing a polyisocyanate componentin combination with an isocyanate-reactive such as a polyhydroxylcomponent or a polyamine are known. These coating compositions aresuitable for the formation of high quality coatings and can be adjustedto produce coatings which are hard, elastic, abrasion resistant, solventresistant and weather resistant.

Generally, there are two mechanisms by which the curing of polyureacoating compositions takes place—moisture cure or plural component “fastcure” which involves cross-linking the polyisocyanate component with anamine. Aliphatic coating compositions which rely upon moisture curedemonstrate very slow curing times which can limit their use in someapplications. Coating compositions which rely upon plural “fast cure”are susceptible to adhesion problems when the curing proceeds tooquickly.

In accordance with the present invention, polyurea coating compositionsbased on a two component system of a polyisocyanate component and apolyaspartic ester isocyanate-reactive component are produced whichdemonstrate a dual cure phenomena which results in improved filmproperties and curing times.

SUMMARY OF THE INVENTION

According to other features, characteristics, embodiments andalternatives of the present invention which will become apparent as thedescription thereof proceeds below, the present invention provides apolyurea coating composition that exhibits a dual cure phenomena, thepolyurea coating composition including:

a polyaspartic ester; and

a polyisocyanate,

wherein the polyisocyanate is present in an amount that is greater thana normal stoichiometric amount for the polyaspartic ester.

The present invention further provides a method of preparing a polyureacoating composition which involves:

providing a polyaspartic ester;

providing a polyisocyanate; and

mixing the polyaspartic ester and the polyisocyanate together so thatthe polyisocyanate is present in an amount that is greater than a normalstoichiometric amount for the polyaspartic ester.

The present invention also provides a surface finish which comprises acured composition that includes a polyaspartic ester and apolyisocyanate, wherein the polyisocyanate is present in an amount thatis greater than a normal stoichiometric amount for the polyasparticester prior to curing.

The present invention still further provides a method for forming asurface finish which involves:

providing a polyaspartic ester;

providing a polyisocyanate;

mixing the polyaspartic ester and the polyisocyanate together so thatthe polyisocyanate is present in an amount that is greater than a normalstoichiometric amount for the polyaspartic ester;

applying the mixed composition to a surface to form a surface coating;and

allowing the applied surface coating to cure.

DETAILED DESCRIPTION OF THE INVENTION

The polyurea coating compositions of the present invention provide ahybrid curing system that combines the “fast cure” of a polyasparticester polyurea reaction with the enhanced adhesion and superior filmproperties of a slower curing moisture cure polyurea. The polyureacoating compositions of the present invention demonstrate enhancedadhesion, rapid cure rates and light stability, and can be used toproduce bubble free, low to high film builds with thicknesses that rangefrom less than 1 mil to greater than 20 mil.

The coating compositions of the present invention comprise two componentpolyureas that have exceptional direct-to-substrate adhesion and arebased the use of a polyaspartic ester that is over indexed with apolyisocyanate. One component is a polyaspartic ester based componentthat can be pigmented or clear and incorporated with or withoutsolvents. The other component is a polyisocyanate that can beincorporated with or with out solvents.

Suitable polyisocyanates for use in accordance with the presentinvention include aliphatic polyisocyanates such ashexamethylenediisocyanate (HDI) and lysine diisocyanate; alicyclicpolyisocyanates such as dicyclohexylene diisocyanate, isophoronediisocyanate (IPDI), cyclohexane diisocyanate (CHDI); aromaticpolyisocyanates such as tolylene diisocyanate (TDI), diphenylmethanediisocyanate (MDI), naphthylene diisocyanate (NDI), xylylenediisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); andmixtures thereof. Higher functional Biruet polyisocyanates are usuallypreferred over trimers, dimers, and hexamethylenediisocyanate (HDI) wasfound to be particularly useful for purposes of the present invention.

In formulating the coating compositions of the present invention, thepolyaspartic ester is over indexed with an aliphatic polyisocyanate.That is, the polyisocyanate was used in an amount that is greater thanthe stoichiometric amount one would normally calculate for a specificamount of a polyaspartic ester. During the course of the invention, theapplicant determined that measurable improvements in the film propertiesof a coating produced from the polyurea coating compositions of thepresent invention were obtained at an over indexing of the polyasparticester to a polyisocyanate at above about 1.5 NCO to NH. Optimum filmproperties were obtained without the use of a secondary catalyst at anover indexing of the polyaspartic ester to a polyisocyanate at aboveabout 2.5±0.5 NCO to NH. When over indexing the polyaspartic ester witha polyisocyanate above about 3.0 NCO to NH, without the use of asecondary catalyst, the air dry cure times increase unfavorably.

Although not intending to be bound by any particular theory, andunderstanding that an applicant need not comprehend the scientificprinciples on which the practical effectiveness of his invention rests,applicant theorizes that by selectively over indexing the polyasparticester to the polyisocyanate, it is possible to reach an optimum balancebetween moisture curing and “fast curing” which involves cross-linkingthe polyisocyanate component with an aliphatic amine. When the mechanismof moisture curing predominates, surface adhesion is optimized; however,the curing times are very long and the film is susceptible to theformation of CO₂ bubbles when the applied dried film thickness exceeds 5mil, or under high humidity conditions. When the cross-linking mechanismassociated with fast curing predominates, surface adhesion is reduced infavor of quicker curing times. Applicant has determined that within anover indexing range of from about 1.5 up to about 3.0 of NCO to NH, thepolyurea coating compositions of the present invention demonstrate adual cure property in which the cross-linking mechanism associated withfast curing causes the surface of a coating to dry relatively fast,while the mechanism of moisture curing at the interface between thecoating layer and substrate allows the coating composition to cure moreslowly and thereby develop good adhesive properties.

The polyurea coating compositions of the present invention can beapplied to virtually any surface as a wet coating which can be appliedin any conventional manner such as spraying, dipping, brushing, etc.Once applied, if desired, the coatings can be air dried or forced driedaccording to conventional methods. The coating compositions can besuitably applied over a temperature range of about 40° F. to about 95°F. and relative humidity levels of about 40% to about 95%.

The polyurea coating compositions of the present invention have beenfound to produce finishes that have strong adhesion properties, hightensile strengths, chemical resistance to solvents and other chemicalagents, resistance to ultraviolet light, and excellent color and glossretention. The finishes are hard as well as impact and chip resistant,and can be recoated as desired.

It is noted that the polyurea coating compositions can include singlepolyaspartic esters or blends of polyaspartic with or without additionalcatalytic agents. In addition, the compositions can include otherconventional components such as pigments, dyes, fillers, carriers,solvents, surface texturing agents, etc. For convenience of field use,the two components of the compositions can be formulated to be mixed ina 1:1 ratio. Such a mixing ratio eliminates the need for measuringdifferent amounts of the two components. The coating compositions havebeen determined to be particularly useful as an alternative toconventional coatings that require baking, when the parts or articles tobe coated are too large or otherwise unsuitable for baking.

The following non-limiting examples were conducted to evaluateperformance characteristics of the polyurea coating compositions of thepresent invention. The polyurea coating compositions tested in thefollowing examples were non-pigmented clear coats that were applied at adry film thickness (DFT) of 2 mil. The coating compositions were batchmixed and air spray applied.

Performance characteristics in the examples were evaluated using thefollowing evaluation scale (ranging from 0 to 5):

0=Total Failure

1=Near Total Failure

2=Partial Failure

3=Marginal

4=Acceptable

5=Excellent

EXAMPLE 1

Crosshatch Adhesion

In this Example, non-pigmented coatings were tested according to theprocedure set forth in ASTM 1-3359-95, Test Method B. The test resultsare presented in Table 1 below:

TABLE 1 Bonderite 1000 Pre- Stoichiometric Untreated Cold Treated ColdRolled Grit Blasted Index Rolled Steel Steel Steel 1.00 0 4 2 1.25 0 4 21.50 1 5 3 1.75 2 5 4 2.00 3 5 4 2.25 4 5 5 2.50 5 5 5 2.75 5 5 5 3.00 55 5

EXAMPLE 2

Conical Mandrel

In this Example, non-pigmented coatings were tested according to theprocedure set forth in ASTM D 522-93, Test Method A. The test resultsare presented in Table 2 below.

TABLE 2 Bonderite 1000 Pre- Stoichiometric Untreated Cold Treated ColdRolled Grit Blasted Index Rolled Steel Steel Steel 1.00 0 3 N/A 1.25 0 4N/A 1.50 0 4 N/A 1.75 1 5 N/A 2.00 2 5 N/A 2.25 4 5 N/A 2.50 5 5 N/A2.75 5 5 N/A 3.00 5 5 N/A

EXAMPLE 3

Recoat, Chemical Resistance and Drying

In this Example, non-pigmented coatings were tested according to theprocedures set forth in ASTM D 3359-95, Test Method B (for recoat) andASTM D 1308-87 (for Chemical resistance using n-methylN-methylpyrrolidinone (NMP),37% HCl, 20% HCl, 100% acetic acid and 50%acetic acid). In addition, drying characteristics were tested asindicated. The test results are presented in Table 3 below

TABLE 3 Recoat After Chemical Dry to Handle 48 Hour Cure: Resistance AirDry @ 72° F. Stoichiometric Intercoat After 30 and 40% Relative IndexAdhesion Day Cure Humidity @ 2 mils DFT 1.00 0 2 <30 Minutes 1.25 1 3<45 Minutes 1.50 2 3 <45 Minutes 1.75 3 3 <45 Minutes 2.00 4 4 <45Minutes 2.25 5 4 <60 Minutes 2.50 5 5 <60 Minutes 2.75 5 5 <75 Minutes3.00 5 5 <120 Minutes 

EXAMPLE 4

Exposure to UV Light

In this Example, Gloss White coatings were tested according to theprocedure set forth in ASTM D 4587-91, Procedure A (8 hour UV/70° C.followed by 4 hour CON/50° C.). The test results are presented in Table4 below

TABLE 4 42 Day 42 Day Stoichiometric Index QUV-B 60 Gloss QUV-B Delta E1.00-89.9 Gloss White 52.1 0.609 2.50-96.2 Gloss White 79.7 0.411

From the above Examples, it can be seen that the properties of thepolyurea coating compositions of the present invention begin improvingas the polyaspartic ester is over indexed with polyisocyanate at above a1.00 and continues to improve up to a stoichiometric index of about2.25, after which the properties maintain the level of improvement.

Although the present invention has been described with reference toparticular means, materials and embodiments, from the foregoingdescription, one skilled in the art can easily ascertain the essentialcharacteristics of the present invention and various changes andmodifications can be made to adapt the various uses and characteristicswithout departing from the spirit and scope of the present invention asdescribed above and set forth in the following claims.

What is claimed is:
 1. A non-aqueous polyurea coating composition thatexhibits a dual cure phenomena, said polyurea coating compositioncomprising: a blend of polyaspartic esters; and a polyisocyanate,wherein the polyaspartic ester is over indexed with the polyisocyanateabove 1.5 of NCO to NH.
 2. A non-aqueous polyurea coating compositionaccording to claim 1, wherein the polyisocyanate is a member selectedfrom the group consisting of aliphatic polyisocyanates, alicyclicpolyisocyanates, aromatic polyisocyanates, and mixtures thereof.
 3. Anon-aqueous polyurea coating composition according to claim 2, whereinthe polyisocyanate comprises an aliphatic polyisocyanate.
 4. A method ofpreparing a non-aqueous polyurea coating composition which comprises:providing a blend of polyaspartic esters, providing a polyisocyanate;and mixing the polyaspartic ester and the polyisocyanate together sothat the polyisocyanate is present in an amount that is greater than anormal stoichiometric amount for the polyaspartic ester, wherein thepolyaspartic ester is over indexed with the polyisocyanate above 1.5 ofNCO to NH.
 5. A surface finish which comprises a cured coating thatincludes a non-aqueous polyurea coating composition comprising a blendof polyaspartic esters and a polyisocyanate, wherein the polyasparticester component is over indexed with the polyisocyanate above 1.5 of NCOto NH.
 6. A surface finish according to claim 5, wherein thepolyisocyanate is a member selected from the group consisting ofaliphatic polyisocyanates, alicyclic polyisocyanates, aromaticpolyisocyanates, and mixtures thereof.
 7. A surface finish according toclaim 6, wherein the polyisocyanate comprises an aliphaticpolyisocyanate.
 8. A method for forming a surface finish whichcomprises: providing a polyaspartic ester; providing a polyisocyanate;mixing the polyaspartic ester and the polyisocyanate together withoutthe addition of water so that the polyisocyanate is present in an amountthat is over indexed with the polyisocyanate above 1.5 of NCO to NH,applying the mixed composition to a surface to form a surface coating,wherein the mixed composition cures dry to handle after air drying 72°F. and 40% relative humidity in less than 120 minutes and allowing theapplied surface coating to cure.
 9. A method for forming a surfacecoating according to claim 8, wherein the polyisocyanate is a memberselected from the group consisting of aliphatic polyisocyanates,alicyclic polyisocyanates, aromatic polyisocyanates, and mixturesthereof.
 10. A method for forming a surface coating according to claim9, wherein the polyisocyanate comprises an aliphatic polyisocyanate. 11.A non-aqueous polyurea coating composition that exhibits a dual curephenomena, said polyurea coating composition comprising: a polyasparticester; and a polyisocyanate, wherein the polyisocyanate is present in anamount that is greater than a normal stoichiometric amount for thepolyaspartic ester, such that the coating composition provides a hybridcuring system that combines the fast cure of a polyaspartic esterpolyurea reaction with the enhanced adhesion and superior filmproperties of a slower moisture cure polyurea, wherein the coatingcomposition cures dry to handle after air drying at 72° F. and 40%relative humidity in less than 120 minutes.
 12. A non-aqueous polyureacoating composition according to claim 11, wherein the polyasparticester is over indexed with the polyisocyanate above 1.5 of NCO to NH.13. A non-aqueous polyurea coating composition according to claim 11,wherein the polyaspartic ester comprises a blend of polyaspartic esters.14. A non-aqueous polyurea coating composition according to claim 11,wherein the polyisocyanate is a member selected from the groupconsisting of aliphatic polyisocyanates, alicyclic polyisocyanates,aromatic polyisocyanates, and mixtures thereof.
 15. A non-aqueouspolyurea coating composition according to claim 14, wherein thepolyisocyanate comprises an aliphatic polyisocyanate.
 16. A surfacefinish which comprises a cured coating of a non-aqueous polyurea coatingcomposition comprising a polyaspartic ester and a polyisocyanate,wherein the polyisocyanate is present in an amount that is greater thana normal stoichiometric amount for the polyaspartic ester prior tocuring, such that the coating compositions provides a hybrid curingsystem that combines the fast cure of a polyaspartic ester polyureareaction with the enhanced adhesion and superior film properties of aslower moisture cure polyurea wherein the coating composition cures dryto handle after air drying at 72° F. and 40% relative humidity in lessthan 120 minutes.
 17. A surface finish according to claim 16 wherein thepolyaspartic ester is over indexed with the polyisocyanate above 1.5 ofNCO to NH.
 18. A surface finish according to claim 16, wherein thepolyaspartic ester comprises a blend of polyaspartic esters.
 19. Asurface finish according to claim 16, wherein the polyisocyanate is amember selected from the group consisting of aliphatic polyisocyanates,alicyclic polyisocyanates, aromatic polyisocyanates, and mixturesthereof.
 20. A surface finish according to claim 19, wherein thepolyisocyanate comprises an aliphatic polyisocyanate.